The general objective of this research proposal is to examine the processes which regulate the synthesis and degradation of myofibrillar proteins in the rat myocardium at the level of translation. The turnover of individual myofibrillar proteins will be studied particularly those proteins involved in the regulation of contraction such as tropomyosin and the troponin complex. Changes in the synthesis and degradation of individual myofibrillar proteins will also be evaluated during development when significant growth occurs, following starvation and refeeding and also during the development of cardiac hypertrophy following the imposition of an acute stress. This study should provide insights into the possible differential response of individual myofibrillar proteins to conditions which affect protein metabolism. We will also evaluate the role of synthesis and degradation in the accumulation or loss of protein from the tissue. Levels of ribosomes active in protein synthesis will also be correlated with changes in synthesis and degradation in an effort to distinguish between effects on peptide chain initiation and elongation. The role of changes in the level of charged tRNA in regulating protein synthesis and degradation will be evaluated. Lysosomal protease activities and neutral protease activity will also be determined as an index of the degradative capacity of the tissue.